Knife gate valves are well known in the art for use in a variety of applications in a broad range of industries, including but not limited to, pulp & paper, chemical, petroleum refining, mining, iron and steel manufacture, waste water, power generation, food and beverage, and marine applications. In particular, knife gate valves are advantageous for use in non-abrasive and abrasive slurry applications and for large diameter water applications. The use of elastomeric valve seats are known to be particularly helpful for applications having high solids or prone to scaling.
One advantage of knife gate valves is the ability to cut through slurries, scale, and surface build ups. Another advantage is the unobstructed flow path, which not only provides high flow capacity, but also allows large objects to safely pass through the valve. Small face-to-face dimensions reduce the weight of the valve and facilitate piping design. Knife gate valves are typically available in sizes as small as 2″ diameter to specially fabricated valves exceeding 100″ in diameter.
Disadvantages of knife gate valves historically have been a general inability to provide a tight shut off and the presence of cavities within the valve that promote contamination of the fluid stream. The use of elastomeric transverse seals has increased the ability of knife gate valves to provide a tighter shut off. In particular, U.S. Pat. Ser. No. 10/816,520, incorporated herein by reference, owned by the common assignee of the present invention, and listing as a Co-inventor Paul Comstock, who is also a listed inventor of the present invention, discloses a combined transverse seal/perimeter seal in which the transverse seal is adapted to receive an injectable packing material, which provides an improved seal.
Because slurries can be abrasive and sometimes corrosive, knife gate valves used in such service may have a liner to protect the valve body. Some valves have internally bonded liners, whereas others use a single-piece or multi-piece replaceable liner clamped between two separate body halves. In designs in which the liner material extends to the mating flanges between which the valve is mounted, the liner material may create the seal between the valve and the mating flanges. If the face of the liner that contacts the mating flanges becomes damaged, however, and the seal is compromised, overtightening the flanges to reduce leaking at the flange may compress the liner against the gate. This compression of the liner against the gate can increase actuation forces for the gate and may lead to premature failure of the liner. Thus, there is always a need in the art to improve durability and seal quality of lined gate valves.